The present invention relates to improvements in an automatic document feeder used for a recording device or an image reading device of an electrophotographic copier, and more particularly relates to improvements in a circulation type automatic document feeder having a document feeding mode (RDH) in which one-sided or two-sided documents stacked on a document stack section are separated from the document stack one by one and fed to an image reading section and then the document is returned to the document stack section so that it can be repeatedly fed, and also having a two-sided document reversal feeding mode (R-RDH).
An automatic document feeder (ADF) that can efficiently and automatically feed a document on which an image is recorded, has already been provided to a recording device of an electrophotographic copier or a recorded image reading apparatus.
An automatic document feeder (RADF) having a reversal function by which a document is reversed, is put into practical use as a copier by which the images on a two-sided document are copied onto one side or both sides of a recording paper and as an image reading apparatus by which the images are read.
Also, a circulation type automatic document feeder (RDH) has been proposed in which the documents stacked on a document stack section are separated one by one and automatically fed onto a platen glass and the document exposed on the platen glass is returned to the document stack section so that the document can be repeatedly processed.
By this circulation type automatic document feeder (RDH), a copy is made when a document is circulated once, so that the document is circulated by the number of required copies.
Moreover, a circulation type automatic document feeder (R-RDH) has been also provided in which a document reversal mechanism is added to the RDH described above (disclosed in Japanese Patent Application No. 20228/1988).
By these circulation type automatic document feeder (RDH and R-RDH), which will be referred to as RDH hereinafter, it is possible to conduct a high speed continuous copying operation and to quickly collate copied recording papers. Moreover, when the circulation type automatic document feeder (RDH) is combined with a finisher device by which stapling and punching operations are conducted on the recording papers, the overall recording operation can be automatically performed.
The aforementioned RDH device is of a bottom-feed-top-return type in which: a plurality of documents are stacked on the document stack section under the condition that the front surfaces of the documents are set upward; and the lowermost document is separated from the document stack one by one and conveyed to the processing section (the platen glass surface).
In the bottom-feed-top-return type apparatus described above, when a document is sent out from the document stack, the front surface of a document and the back surface of another document are rubbed with each other, so that the image on the rubbed document is damaged and further the front and back surfaces of a document are stained. Especially when a document is written with a pencil, the document is remarkably stained.
In order to solve the above problems, a top-feed-bottom-restack type RDH apparatus has been disclosed in Japanese Patent Publication No. 37536/1981. In this apparatus, a processed sheet is inserted under the sheet stack with a cyclic operation type stack lifting means.
The following problems may be encountered in the top-feed-bottom-restack type RDH.
(1) Structure of the cyclic operation type lifting means is complicated.
(2) In the case where an end portion of a sheet to be inserted under the stack is curled, there is a high possibility that the end portion is caught by the cyclic operation type stack lifting means.
(3) When a sheet is returned at high speed, the operation of a document feeder becomes complicated, so that the operation becomes unstable.
(4) Each time a sheet is returned, the stack lifting means is moved upward and downward, so that noises are caused.
(5) It is difficult to adjust the apparatus when the sheet size is changed.
In order to overcome the above disadvantages, the invention disclosed in Japanese Patent Publication Open to Public Inspection No. 403220/1990 is constituted in the following manner: The circulation type top-feed-bottom-return automatic document feeder includes an upper suction fan means, an upper feeding belt type document feeding means, and a lower document return rotation means composed of a plurality of thin belts.
However, in the automatic document feeder constituted in the aforementioned manner, the following problems may be encountered, so that improvements are required.
(1) Noises are caused by the suction fan means, and its manufacturing cost is high.
(2) In the structure in which a plurality of thin belts are disposed, a document conveyed on the belts is not uniformly contacted with the belts because there are gaps between the belts, so that the document surface is formed into a wave-shape, and the protruded portions at the leading end of the document on the belts collide with the trailing end of an upper document. As a result, documents are jammed.
In order to overcome the aforementioned disadvantages, the first object of the present invention is to provide a circulation type automatic document feeder of an upper-feed-bottom-insertion system that can be stably operated even when documents are fed at high speed and further the document feeder can handle various sizes of documents.
In addition to the aforementioned apparatus, the sheet accommodation and supply apparatus disclosed in Japanese Patent Publication Open to Public Inspection No. 205273/1991 is constituted in the following manner: In an RDH device, a return document is reversed and inserted into the bottom of a document bundle on the downstream side of document feed; and a vertical press member is provided in the upper rear end position of the document bundle.
In the aforementioned automatic document feeder having the RDH mode and R-RDH function, it is necessary to provide a separation means to separate a document conveyed out from the image reading means and stacked again on the document stack section, from a document bundle previously stacked on the document stack section.
In the conventional bottom-feed-top-return type RDH device, the separation means is composed of a simple lever lightly coming into contact with the upper surface of a document bundle. However, in the RDH device of the top-feed-bottom-return system, it is necessary to provide a movable separation means below the lowermost sheet of the document bundle. Accordingly, there is a possibility that the separation means interferes with a document to be conveyed by the document feed means. Especially in the RDH device operated at high speed, it is necessary to stabilize the operation of the document separation means.
The present invention overcomes the disadvantages of the conventional automatic document feeder. The second object of the present invention is to provide an automatic document feeder having an RDH device of the top-feed-bottom-return system in which a document separation means is provided that can be positively advanced and withdrawn below the lowermost document to be circulated.